137 lines
4.5 KiB
Go
137 lines
4.5 KiB
Go
// Copyright (c) 2013-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package wire
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import (
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"fmt"
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"io"
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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)
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// MsgGetHeaders implements the Message interface and represents a bitcoin
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// getheaders message. It is used to request a list of block headers for
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// blocks starting after the last known hash in the slice of block locator
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// hashes. The list is returned via a headers message (MsgHeaders) and is
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// limited by a specific hash to stop at or the maximum number of block headers
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// per message, which is currently 2000.
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//
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// Set the HashStop field to the hash at which to stop and use
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// AddBlockLocatorHash to build up the list of block locator hashes.
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//
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// The algorithm for building the block locator hashes should be to add the
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// hashes in reverse order until you reach the genesis block. In order to keep
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// the list of locator hashes to a resonable number of entries, first add the
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// most recent 10 block hashes, then double the step each loop iteration to
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// exponentially decrease the number of hashes the further away from head and
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// closer to the genesis block you get.
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type MsgGetHeaders struct {
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ProtocolVersion uint32
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BlockLocatorHashes []*chainhash.Hash
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HashStop chainhash.Hash
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}
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// AddBlockLocatorHash adds a new block locator hash to the message.
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func (msg *MsgGetHeaders) AddBlockLocatorHash(hash *chainhash.Hash) error {
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if len(msg.BlockLocatorHashes)+1 > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message [max %v]",
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MaxBlockLocatorsPerMsg)
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return messageError("MsgGetHeaders.AddBlockLocatorHash", str)
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}
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msg.BlockLocatorHashes = append(msg.BlockLocatorHashes, hash)
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return nil
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}
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// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
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// This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) BtcDecode(r io.Reader, pver uint32) error {
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err := readElement(r, &msg.ProtocolVersion)
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if err != nil {
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return err
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}
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// Read num block locator hashes and limit to max.
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count, err := ReadVarInt(r, pver)
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if err != nil {
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return err
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}
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if count > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message "+
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"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
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return messageError("MsgGetHeaders.BtcDecode", str)
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}
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// Create a contiguous slice of hashes to deserialize into in order to
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// reduce the number of allocations.
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locatorHashes := make([]chainhash.Hash, count)
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msg.BlockLocatorHashes = make([]*chainhash.Hash, 0, count)
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for i := uint64(0); i < count; i++ {
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hash := &locatorHashes[i]
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err := readElement(r, hash)
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if err != nil {
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return err
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}
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msg.AddBlockLocatorHash(hash)
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}
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return readElement(r, &msg.HashStop)
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}
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// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
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// This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) BtcEncode(w io.Writer, pver uint32) error {
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// Limit to max block locator hashes per message.
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count := len(msg.BlockLocatorHashes)
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if count > MaxBlockLocatorsPerMsg {
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str := fmt.Sprintf("too many block locator hashes for message "+
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"[count %v, max %v]", count, MaxBlockLocatorsPerMsg)
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return messageError("MsgGetHeaders.BtcEncode", str)
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}
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err := writeElement(w, msg.ProtocolVersion)
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if err != nil {
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return err
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}
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err = WriteVarInt(w, pver, uint64(count))
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if err != nil {
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return err
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}
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for _, hash := range msg.BlockLocatorHashes {
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err := writeElement(w, hash)
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if err != nil {
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return err
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}
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}
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return writeElement(w, &msg.HashStop)
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}
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// Command returns the protocol command string for the message. This is part
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// of the Message interface implementation.
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func (msg *MsgGetHeaders) Command() string {
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return CmdGetHeaders
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}
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// MaxPayloadLength returns the maximum length the payload can be for the
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// receiver. This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) MaxPayloadLength(pver uint32) uint32 {
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// Version 4 bytes + num block locator hashes (varInt) + max allowed block
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// locators + hash stop.
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return 4 + MaxVarIntPayload + (MaxBlockLocatorsPerMsg *
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chainhash.HashSize) + chainhash.HashSize
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}
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// NewMsgGetHeaders returns a new bitcoin getheaders message that conforms to
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// the Message interface. See MsgGetHeaders for details.
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func NewMsgGetHeaders() *MsgGetHeaders {
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return &MsgGetHeaders{
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BlockLocatorHashes: make([]*chainhash.Hash, 0,
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MaxBlockLocatorsPerMsg),
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}
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}
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